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Atlantic Tropical Weather Discussion

AXNT20 KNHC 261726

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
126 PM EDT Wed Jul 26 2017

Tropical Weather Discussion for North America, Central America
Gulf of Mexico, Caribbean Sea, northern sections of South
America, and Atlantic Ocean to the African coast from the
Equator to 32N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 1200 UTC surface analysis and satellite imagery through 
1715 UTC.


A tropical wave is over the easter Atlantic with axis extending 
from 16N26W to 06N26W, moving westward at 10 kt. Although 
TPW imagery shows that the wave is in an area of moderate to deep
moisture, it remains under Saharan dry air and dust at lower 
levels inhibiting significant convection. A few showers are
observed along the waves axis mainly below the monsoon trough
south of 12N between 22W-28W. 

A tropical wave is in the central Atlantic with axis extending 
from 12N36W to 04N36W, moving westward at about 5 kt. The SSMI 
Total Precipitable Water imagery (TPW) indicates that deep 
moisture prevails within this wave. Scattered moderate convection
is where the wave crosses the monsoon trough mainly from 08N-11N
between 35W-38W. 

A large amplitude tropical wave has its axis extending from near 
24N55W to 12N54W, moving westward near 15 kt. The northern 
portion of this wave is observed as a very noticeable area of 
moisture, as seen on SSMI TPW imagery. The wave has a distinct 
signal at 650-700 mb as suggested in global model guidance. 
Saharan dry air and dust is following the wave, as noted in the 
latest METEOSAT-9 imagery. Scattered showers are observed along
the northern portion of the wave mainly north of 22N between

An eastern Caribbean tropical wave has its axis along 66W between
06N-18W, moving westward at 10-15 kt. The wave has a distinct 
moist area as seen on SSMI TPW imagery. A broad 700 mb troughing 
is covering much of the eastern Caribbean. At this time, dry air
dominates the eastern portion of the Caribbean therefore, no 
convection is related to this wave. 


The monsoon trough extends from 13N16W to 09N35W. The ITCZ begins
near 08N41W and continues to 10N61W. Besides convective activity 
described above in association with the tropical waves, scattered 
moderate convection is within 60-90 nm north of the ITCZ between 



A broad surface ridge extends across the basin from the east,
anchored by a 1020 mb high centered over northern Florida. A
diffluent flow aloft is supporting scattered moderate convection
along 25N and east of 90W. Another area of scattered moderate
convection prevails over the Bay of Campeche mainly south of 25N 
and west of 94W. Scatterometer data depicts a light to gentle
anticyclonic flow across the basin. Little change is expected 
with the current synoptic pattern over the next couple of days.


A tropical wave is over the eastern Caribbean. Refer to the 
section above details. Scattered moderate convection is quickly 
increasing over the far southwest Caribbean south of 13N and west
of 75W. This activity is due mainly to the presence of the 
monsoon trough that extends from the eastern Pacific to across 
Costa Rica and Panama, and the nearby southern extent of an upper-
level trough that stretches from Hispaniola to the southwest 
Caribbean. Scatterometer data depicts moderate trades across most
of the basin except between 72W-78W where fresh easterlies
prevail. Expect for the tropical wave moving through the eastern 
Caribbean to provide additional moisture and instability to that 
portion of the area over the next 48 hours.


Isolated showers are observed just north of the eastern section 
of the Dominican Republic as an upper-level cyclonic shear axis 
nearby is providing additional instability to an already very 
moist and unstable environment present over the island. Water 
vapor imagery depicts that moisture has increased in the upper- 
levels compared to the previous days. With plenty of deep layer 
moisture and instability in place, and with the added factor of 
the eastern Caribbean tropical wave forecast to pass near the 
island within the next 48 hours, expect for deep convection to 
become scattered to locally numerous over most sections of 
Hispaniola through at least Thursday night. Some of this activity 
may produce locally heavy rain and frequent lightning.


Three tropical waves are moving across the basin. Refer to the
section above for details. The basin is under the influence of a
surface ridge, anchored by a 1026 mb high centered near 32N39W. A
large area of Saharan dust is present over the eastern Atlantic, 
and much of the central Atlantic behind the tropical wave along 
55W. No major changes expected through next couple of days.

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